I've seen in some sites related to blockchain the term "Hardfork". I've read some explanations and couldn't understand them as they were too difficult for my English levels of comprehension. Can you explain it in a better way?

As it relates to blockchain technology, a hard fork (or sometimes hardfork) is a radical change to the protocol that makes previously invalid blocks/transactions valid (or vice-versa), and as such requires all nodes or users to upgrade to the latest version of the protocol software. Put differently, a hard fork is a permanent divergence from the previous version of the blockchain, and nodes running previous versions will no longer be accepted by the newest version. This essentially creates a fork in the blockchain, one path which follows the new, upgraded blockchain, and one path which continues along the old path. Generally, after a short period of time, those on the old chain will realize that their version of the blockchain is outdated or irrelevant and quickly upgrade to the latest version.

A hardfork is a change to the bitcoin protocol that makes previously invalid blocks/transactions valid, and therefore requires all users to upgrade.

Any alteration to bitcoin which changes the block structure (including block hash), difficulty rules, or increases the set of valid transactions is a hardfork. However, some of these changes can be implemented by having the new transaction appear to older clients as a pay-to-anybody transaction (of a special form), and getting the miners to agree to reject blocks including the pay-to-anybody transaction unless the transaction validates under the new rules. This is known as a softfork, and how P2SH was added to Bitcoin.

@Manandezo
Due to the upsurge in the volume of transactions (blocks) in the bitcoin entire database (blockchain) which has created possible backlogs and has become a source of worry to the bitcoin virtual currency online community which believes that in the near future there could be problems of control, management, transparency and fraud.

The online community has adopted a change of approach and procedure in the management of bitcoin transactions or blocks which make up the blockchain. This change is called hardfork.

Because the blockchain are constantly growing as ‘completed’ blocks are added to it, the key miners and developers of bitcoin have agreed to adopt a new way of operating the cryptocurrency (hardfork).The new technology, called Segwit2x, has gradually been adopted by key players against the old rival system called Bitcoin Cash.

Therefore, the event in which Bitcoin split into two: Segwit2x and Bitcoin Cash in it’s bid to manage the high traffic in the growing online transactions that has divided the virtual currency’s online community is known as Hardfork.

Thus, a hard fork can be implemented to correct important security risks found in older versions of the software, to add new functionality, or to reverse transactions

Segwit2x proposes moving some of bitcoin’s transaction data outside of the block and on to a parallel track to allow more transactions to take place. After that happens, blocks would double in size some time in November.

Bitcoin Cash does not propose moving transaction data outside of each block, but wants to increase the size of each to 8MB. Its backers are sceptical that the Segwit2x plan will follow through with doubling the block size later on.